What is a 'Wing Loop Fault' on an A320 series Aircraft?

Question

I was recently involved in a flight that had issues before take off. The plane was an Airbus 321.

It was explained to me as being a "wing loop fault". The problem was that the ECAM messages were displayed differently each time and were inconsistent. The flight was aborted just before take off (for safety reasons) but the problem was fixed soon after by replacing a part.

Can anyone explain this problem with the wing loop to me in more detail. What could have gone wrong and what was the likely fix.

Also, what maintenance and pre-flight checks should occur on the "wing loop"?

Sorry for any vagueness in my question, I didn't receive much information.

---

Edits

• This was on aircraft G-OMYJ around the 24th August 2013
• My route was (EMA) --> (DLM), flight TCX5894. But the fault may have occurred on the previous flight. The details are unfortunately hazy. Is there anyway of me finding the whereabouts of the plane in the days leading up to this incident?

Answer 1

My guess is that there was some circuitry that was playing up. While I'm not sure about 'Wing Loops' specifically, for what I think is a similar example the Airbus A320 series has fire loops in the engines.

There are two fire loops. If I'm right, it's got little thermal sensors along way, which disrupt the current if they get too hot (or if the wire is broken). Logic gates ensure that both loops must be 'high' for the fire warning to go off. If one is not working, it works from a single input.

Assuming both of these were working from the beginning, I think it throws a FIRE DET FAULT warning on the pilot information display if one triggers without setting off the other one. I'd imagine that maintenance either disabled the faulty loop within those allowed by the Minimum Equipment List or by changing the part. If it was quick, it was probably the first, but they're not going to go telling passengers that they disabled safety equipment :)

Answer 2

Wing loop fault refers to the overheat/leak detection system running along pneumatic lines in the wings and belly. Fire loops on the engines is a different matter. The loops consist of an outer and inner conductor separated by a "salt", when the loop gets warm, the salt becomes conductive and makes a circuit between the inner and outer conductor. The system often contains of two parallel loops, both has to detect a leak in order to give a warning to the pilot. If only one detects an overheat it gives a fault. The fault can also be triggered by a high resistance in the system, monitored by the BMC . Bleed Monitoring Computer. The system is build up by a lot of elements, and the connection between each element can be a bit "flimsy", making it difficult to perform a proper troubleshooting on.

Answer 3

It might be a problem with the loops of sensors for the fire detection systems etc

For example: ECAM message "FIRE LOOP A FAULT" (ATA 49: APU)

Both engines and the APU each have two identical loops, A & B and a computer- FDU (Fire Detection Unit). A fire warning is given when both loops reach the proper overheat condition. If one loop fails the other loop is able to generate the warning by itself. A fire warning is given if both loops fail within 5 seconds of each other.

...

The leak detection system uses a single loop for the pylons and APU to detect hot air temps associated with duct leaks. Dual loops are used for the wings. If both of the dual loops detect a leak a warning is given, unless there is a fault on one, then only one loop is required to give a warning.

From Eric Parks training notes.

Answer 4

A loop fault is to do with the leak detection system for the pneumatics. As per the FCOM:

Leak detection loops detect any overheating near the hot air ducts in the fuselage, pylons, and wings.

For the pylon and the wing, the sensing elements are tied to form a double loop and for the APU, a single loop.

When the two wing/pylon loops detect a leak, or when one loop detects the leak and the other one is inoperative, they activate a wing/pylon leak signal.

BMC1 and BMC2 each contain identical control logic for the system.

A wing leak signal causes :

• the bleed valve on the related side to close automatically

• the associated FAULT light on the AIR COND panel to come on

• the x-bleed valve to close automatically (except during an engine start)

• the APU bleed valve to close automatically if the APU bleed valve is open and if the leak concerns the left wing (except during engine start).

A pylon leak signal causes :

• the bleed valve on the related side to close automatically

• the FAULT light for the related engine on the AIR COND panel to come on

• the x-bleed valve to close automatically (except during an engine start).

• the APU bleed valve to close automatically if the APU bleed valve is open and if the leak concerns the pylon 1 (except during engine start).

An APU leak signal causes :

• the APU bleed valve to close automatically (except during engine start).

• the FAULT light the APU BLEED pushbutton switch on the AIR COND panel to come on

• the x-bleed valve to close automatically (except during an engine start).